1. Field of the Invention
The present invention relates to a method and a system for the assembly of works and a method for the assembly of automotive vehicles. More particularly, the invention relates to methods and systems suitable for automations the assembly line for assembling automotive vehicles.
2. Description of the Related Art
The assembly line for automotive vehicles is roughly broken down into a white vehicle body assembly line, a coating line and a vehicle body assembly line.
The white body assembly line is to assemble a white vehicle body section temporarily with doors, an engine hood, a trunk lid and so on, prior to coating. In the coating line, the resulting white vehicle body section is coated with a sealing agent and then with undercoating, intermediate coating and overcoating paints, as needed. After coating, the parts such as the doors, the engine hood, the trunk lid and so on are detached from the coated vehicle body section, and each of the parts is transferred and conveyed to the corresponding working lines.
In each of the working lines, various parts, members or units are mounted to the vehicle body sections, doors, engine hoods, trunk lids and so on, and the working lines constitute part of the vehicle assembly line. After the various parts have been mounted to the vehicle body section, the doors, the engine hood, the trunk lid and so on in the corresponding working lines, then the doors, the engine hood, the trunk lid and other members are mounted to the vehicle body section. Further, lower parts such as exhaust system members, suspension members and so on to be mounted to the floor rear bottom of the vehicle body section in the vehicle body assembly line.
In the working lines, the vehicle body sections are loaded on and conveyed by conveyors or carriages or supported by hanger conveyors and the parts, members, units and so on are mounted to the vehicle body sections with the aid of working robots or by manual operations.
Japanese Utility Model Laid-open Publication (kokai) No. 62-108,183 and Japanese Patent Laid-open Publication (kokai) No. 63-265,779 disclose procedures in which the vehicle body section is divided into an upper vehicle body section and an under vehicle body section containing a floor. To each of the upper vehicle body section and the under vehicle body section are mounted various parts in respective working lines, and then the upper vehicle body section is assembled with the under vehicle body section. These procedures are suitable for the automation of the assembly of the automotive vehicles.
In mounting the various parts to the upper vehicle body section, a plurality of working robots are disposed in the assembly line and the upper vehicle body section is conveyed to the working robots which mount the parts to the upper vehicle body section.
These procedures, however, present problems and suffer from disadvantages in supplying various parts to the working robots disposed in the assembly line for mounting them to the upper vehicle body section.
It is difficult to align the upper vehicle body section with the working robots. When the upper vehicle body section is conveyed, for example, with a conveyor or carriage, the conveyor or carriage should be suspended in a predetermined position in the station where the working robot is disposed. If there would be a deviation in the actual position where the conveyor or carriage has been suspended from the predetermined position, the actual position should be corrected prior to the start of the mounting operations for mounting the parts. In particular, when the conveyor or carriage travels at a high speed, the actual position in which it is suspended may be likely to deviate from the predetermined position or the upper vehicle body section loaded on the conveyor or carriage may be likely to be deviated or departed from its predetermined position during the travelling of the conveyor or carriage. In this case, too, the actual position of the conveyor or carriage and/or the position of the upper vehicle body section, relative to the corresponding working robots, is required to be corrected prior to the start of the mounting operations. Hence, in the conventional assembly line, the conveyors or carriages are needed to travel at a speed as low as possible in order to secure the accurate alignment of the upper vehicle body section with the working robots, however, the low speed of conveying the conveyors or carriages lowers efficiency of mounting the parts to the upper vehicle body sections. The lower the speed at which the conveyors or carriages travel, the lower the efficiency in mounting the parts and eventually the lower the production efficiency.
In the conventional vehicle body assembly lines, the problem arises that the upper vehicle body sections should be conveyed to the working robot intermittently when parts are mounted to the upper vehicle body section with the aid of the working robots which are disposed in the working lines. The working robots should stop working until a fresh upper vehicle body section enters the working station after the working robots have mounted the necessary parts to the previous upper vehicle body section and the previous vehicle body section has departed from the corresponding working stations, when the upper vehicle body section is intermittently conveyed and supplied to the working robot in the working station. As a matter of course, the period of time when the working robots should stop working and wait for the fresh upper vehicle body section is a great factor reducing the working efficiency of the working robots. It is to be noted that this period of time during which the working robots stop working becomes extremely long if the conveyors or carriages are to be conveyed at a low speed.
In addition, the requirements for the correction of the posture or position of the upper vehicle body section relative to the corresponding working robots may exert a great influence upon efficiency in the mounting operations, particularly in mounting large parts such as interior units with the aid of the working robots, for example, to the inside of a cabin section of the upper vehicle body section. If the posture or position of the upper vehicle body section loaded on the conveyor or carriage does not fit to the posture or position of the large parts, it will take a long time to correct the posture or position of the upper vehicle body section relative to the posture or the vertical position of the large part prior to the mounting operations. As a matter of course, a longer period of time for aligning the upper vehicle body section with the large parts impairs the working efficiency of the working robots.
On the other hand, the mounting of the lower parts such as driving system parts including internal combustion engines, exhaust system parts, suspension members and so on requires laborious and time-consuming operations. For example, Japanese Patent Laid-open Publication (kokai) No. 63-265,779 discloses the procedures in which the lower parts in a unit form are mounted to the under vehicle body section and thereafter the under vehicle body section is combined with the upper vehicle body section. When the lower parts are mounted to the under vehicle body section and the resulting under vehicle body section is mounted to the floor member as the upper vehicle body section, however, the lower parts in the unit form attached to the floor member may interfere with the mounting of the under vehicle body section to the upper vehicle body section. Hence, this operation may worsen workability in joining the under vehicle body section with the upper vehicle body section.